Validity of FSTs

How effective are these highly touted field sobriety tests? Consider the research funded by the National Highway Traffic Safety Administration (NHTSA), which resulted in the later adoption of the so-called "standardized" field sobriety tests. In a 1977 study, researchers determined that the three most effective field sobriety tests (FSTs) were walk-and-turn, one-leg stand, and horizontal gaze nystagmus. Yet, even using just these supposedly more accurate tests, the researchers found that 47 percent of the subjects who would have been arrested based upon test performance actually had blood-alcohol concentrations of less than the legal limit of. 10 percent. In other words, almost half of all persons 'failing" the tests were not legally under the influence of alcohol! Burns and Moskowitz, Psychophysical Tests for DWI Arrest: Final Report, DOT-HS-802-424, NHTSA (1977).

In 1981, these same researchers conducted further tests in an attempt to improve the credibility of the proposed "standardized" battery of FSTs. The error rate improved somewhat: The false results dropped to 32 percent-i.e., "only" a third of all persons judged to be guilty by these tests were, in fact, innocent. Tharp, Burns, and Moskowitz, Development and Field Test of Psychophysical Tests for DWI Arrests: Final Report, DOT-HS-805-864, NHTSA (1981). Critics of this second "study," however, point out that the "reliability coefficients" for this self-serving research were far below accepted levels in the scientific community. See Cole and Nowaczyk, Field Sobriety Tests: Are They Designed for Failure?, 79 Perceptual and Motor Skills 99 (1994), where the authors noted, among other problems:

The fact that these tests are largely unfamiliar to most people and not well practiced may make it more difficult for people to perform them. As few as two miscues in performance can result in an individual being classified as impaired because of alcohol consumption when the problem may actually be the result of the unfamiliarity with the test.

And, in fact, it appears the NHTSA-funded researchers used methods that ensured improved reliability figures. Apparently, to reduce the number of borderline subjects (those with blood-alcohol levels of, say, .09 or .11 percent), most of the subjects received either excessive amounts of alcohol so that their BACs were elevated to .15 percent, or very small amounts so that they were below .05 percent.